Help needed with an Akai X-200D capstan motor speed

[redpackman]

I am working on an a Akai X-200D tape deck. I've got transport problems. Both take up and rewind reels work great. However the capstan motor is not working right. I do have a copy of the service manual online.

Symptoms:

1. The motor has a moderate hum.

2. It will not run in 7 1/2 ips mode in either direction. It just sits there. It will run in the two slower modes, but more slowly than it ought to by quite a margin.

3. If playing in 3 3/4 ips mode (but slowly) if I hit the reverse button the capstan motor stalls out. Hit the reverse again and it will go back to playing in forward, but still too slowly...quietly humming.

4. I did try a new motor cap (2 uf 450 v AC). It made NO difference. I assume the sky blue wire is the 2 uf wire and the green wire is the common.

5.Disassembled and cleaned both the speed selection switches on the front center at least.

Is the capstan motor shot, or is there some switch/relay inside I'm missing?

Akai expert's advice would be appreciated.

 

[audiojones]

I'd start by checking all 6 of the spark quenchers on the spark quencher board. These are .033uf capacitors in series with 120 ohm resistors in a little plastic box which absorb the spark that forms across the relay points when the motor changes directions at each speed (3 for forward, 3 for reverse). When one or more of them short out it can cause multiple motor windings to get energized at the same time (very bad since only one set of windings can be powered up at a time of course) which causes the motor to fight itself which leads to all kinds of motor running troubles and overheating.

Look for bulging sides on the plastic cases, signs of overheating, arcing sounds or burning smells. It's not uncommon for those things to go bad and completely short out or start to conduct across like a resistor so take a look at all of the spark quenchers in the machine (it uses a bunch of them, not just the six on the quencher board). If you unsolder and lift one leg of each quencher out of the circuit it can help diagnose the problem in case it's not obvious which one is causing it (if one is causing it that is). You can get replacements at mouser, digikey or Newark supply.

If it's not a bad spark quencher it could be the relay or possibly the motor itself but that would be unusual, spark quenchers would be my first suspect.

Sky blue wire is the common into the cap and green is the feed to the motor but if you used a bipolar poly cap it doesn't matter. White is the 1uf addition cap for 50hz operation but you don't need it for 60hz use.

 

[redpackman]

1. So wiring the motor run cap (2uf 450 volts) with one lead on the sky blue wire and one on the green was OK, then?

2. If the quenchers are not obviously faulty (bulging, burned etc.) Is there a way to test them, if I unsolder one lead? I've tested resistors, transistors, capacitors, diodes but testing these things are new birds to me.

3. Thank you so much for this. I was fearing that the motor was shot. If it's a quencher, it'd be a lot less trouble and expense.

 

[redpackman]

By the way, the Service Manual (online) says that the spark killers that relate to the motor are 0.0033 uf + 120 ohm/500vw. Is that a typo.... 0.0033 uf vs .033 uf?

 

[audiojones]

1. So wiring the motor run cap (2uf 450 volts) with one lead on the sky blue wire and one on the green was OK, then?

2. If the quenchers are not obviously faulty (bulging, burned etc.) Is there a way to test them, if I unsolder one lead? I've tested resistors, transistors, capacitors, diodes but testing these things are new birds to me.

3. Thank you so much for this. I was fearing that the motor was shot. If it's a quencher, it'd be a lot less trouble and expense.

1. I dunno, if you used a non polarized poly cap then like I said it doesn't matter but if you used something else then perhaps it does. I don't know what you put in there.

2. I've never tried testing one but I would imagine there shouldn't be continuity across it. They've always been pretty obvious when bad and by troubleshooting as I mentioned above it should be pretty easy to find the culprit.

3. You're welcome, hopefully it's not the motor but it's still remotely possible. They are pretty robustly built motors and don't go bad often but anything is possible after 45+ years.

The spark quenchers should be 0.033uf and 120 ohms, probably a typo in the manual but look at the actual value stamped on the side of the spark quencher.

 

[redpackman]

OK, unsoldered all the spark killers, leaving only one leg connected, so they were disabled. I checked them all with capacitor tester and they all came pretty close to the .033 uf measurement. None had continuity across them.

With the spark killers still all disconnected the motor runs only in 1/ 7/8 ips and 3 3/4 ips. When I try 7 1/2 ips the motor spins for maybe half a second and then stops dead. It spins freely. It is not a bearing issue, nor is there undue drag on the flywheel it's powering (or it wouldn't run in the two slow speeds).

Any more ideas?

 

[audiojones]

The only other suspects I can think of besides the motor itself would be the speed switch, direction relays and associated wiring. It must deliver 100 volts under load to the capstan motor in either direction at any speed. If you're not getting full voltage to the motor when it's under load then look to the speed switch, direction relays, wiring and connections. Test carefully though as it is 100 volts.

If the motor behaved differently at all on any speed with the spark quenchers lifted then I would suspect one or more are bad or are going bad and they should all be replaced. Hopefully one of the quenchers didn't go bad and wipe out the motor winding for the high speed. Remember these things behave differently under an energized load so don't depend on static resistance and capacitance measurements, often voltage and current strains of live conditions reveal insulation breakdowns etc.

If the other motor speeds still aren't right make sure you have 100 volts coming from the green wire out of the connector to your speed switch. Also make sure the transformer is set for 120 volts and 60hz and check all of the connector plugs for good contact.

 

[redpackman]

The speed switch has been disassembled and cleaned. It registers good conductivity on all its poles. I'm getting 100v on 1/ 7/8 and 3 3/4 ips, but 85 volts when I switch the speed switch to 7 1/ 2. ?????? Are the direction relays dirty? Where are they located? I'll have to look around. It'll play "OK in 3 3/4 ips in forward speed, but if I hit the reverse button the motor just stalls out and hums. Haven't taken a voltage reading under that condition. I usually bail and hit the "forward" button (reverse) again, because that scenario just doesn't seem healthy. I have the transformer set right (120 v 60hz).

I have also tried this with the original motor cap connected and then a new 2 uf 450v motor cap replacing it (between/connected to the green and light blue wires). Made no difference.

 

[audiojones]

Check the spark quencher coming off of the reversing relay between the light green wire and the sky blue wire (labeled cr0201). If that one shorts out it will cause the capstan motor to malfunction. Don't confuse it with the other quencher (labeled cr0202) which is for the reverse direction backtension control, the one you want to check is between terminals 4 and 5 on the schematic. Check the reversing relay contacts too and measure the available voltage when the motor stalls out in reverse, bad relay contacts can cause all of that stuff. A bad spark quencher in the position of cr0201 can cause the motor reversing relay contacts to burn and pit as well as motor troubles due to shorting out.

As a last resort it is possible to connect the 7 1/2 ips winding directly to the 100 volt power supply and the return leg to the common to verify if the motor is bad or if it's the deck controls causing the problem but if it's not the reversing relay quencher or the relay contacts then it's likely to be the motor.

 

[redpackman]

Checked the spark quencher at CR0201. No continuity across it (I detached one end so it was out of circuit). It has capacitance, I believe around 9/10 picofarads. I removed the reversing relay, took off the cover and cleaned the contacts with electric contact cleaner and reassembled it. Continuity is good on all contacts, no visual burning is apparent.

What on earth would cause the voltage at 7/ 12 ips to be around 85 volts when on the other two speeds it's MUCH higher (between 100 and 170volts)?

I have not touched the mute relay (yet). That wouldn't have any effect would it?

 

[audiojones]

Nope, all the muting relay does is cut the amplifier volume for a few seconds after reversing until the motor gets back up to speed and for a few seconds at power up to mute the turn on thump.

The higher motor speed draws more current which can reveal poor contacts or power supply faults. More current draw through a faulty connection would cause a voltage drop and since it was acting differently in reverse vs forward as well as at higher speed the next logical step was to inspect the relay for poor contact and its quencher for a short.

If you are certain that the relay contacts are good and there is no voltage drop across them when it's under load then I guess it's got to be either the capstan motor itself, the wiring / connectors for the power to the capstan motor or the transformer windings used to supply the capstan motor. The windings used for the reel table motors are separate from the ones used for the capstan motor, so they can still be functioning properly even if the capstan motor winding is bad.

I don't think I've ever run across a bad transformer and probably only once a bad motor but as I said before after 45+ years of service who knows? I'm sure Akai never thought these would still be in operation all these years later. I'd sure give all of the wiring and connector ends the once over twice though, there's a lot of switching and connections going on in there. If you've got 100 volts leaving the transformer but only 85 volts at the capstan motor then you've got a flaky connection somewhere. If you've got 85 volts across the whole circuit when it's under a load then either the capstan motor is bad and is dragging the voltage down (usually accompanied by a burning odor, overheating or maybe even smoke) or maybe the transformer is no longer capable of supplying the power needed by the motor under higher load demand conditions.

Don't forget that the load demand is increased quite a bit when you switch it to reverse because the motor has to change direction under a load while the tape is rolling. Because this model of Akai deck doesn't drop the transport carriage down and stop the tape motion when reversing directions there's a lot of torque needed to start it back up in reverse, could be a clue as to where the trouble lies. Does the service manual happen indicate what the motor winding impedance should be? A faulty motor winding should show up when you ohm it out if you know what it's supposed to be.

 

[redpackman]

First of all, Audiojones, I appreciate all this advice and good, experienced counsel. It must drive you nuts to work with a guy who barely knows the difference between AC current and DC.

I've taken some new measurements. Perhaps they'll tell you something. All the readings are in AC.

With the speed selector at 1 7/8 ips: AC voltages: Gray wires on the Spark Quencher Card 32v Brown Wires on the Spark Quencher Card (SQC) 93 v Green wire at the motor cap 169 volts The speed seems to be fairly normal in this setting IF going forward direction only.

With speed selector at 3 3/4 ips: AC voltages : Yellow wires on the SQC 30.7 v Red wires on the SQC 90.2 v Green wire at the motor cap 162 volts. The speed seems to be fairly normal in this setting IF going forward direction only.

With the speed selector at 7 1/2 ips: AC voltages Orange wires at SQC 68.8 volts White wires at SQC 51.8 v Green wire at the motor cap 17 volts. The motor totally stalls in this setting, as you'd expect with these readings.

Interestingly enough at the speed switch when it's set at 7 1/2 ips at the top terminal where the orange wire goes out the reading is 95v IF the orange wire is disconnected from the SQC. There are also 95v at the SQC end of that disconnected wire, but once it's connected to the SQC and thus to the motor the voltage drops as above.

What wires would I use to measure the resistance in the motor windings? There are quite a few....all of the above including green. Which colors do I pair up to measure the motor winding resistance? In the schematic it seems to my very inexperienced eyes to pair up gray and brown for the 1 7/8 ips, yellow and red for 3 3/4 ips and orange and white wires for 7 1/2 ips...then there's green and a purple(?)/pink wire that goes to the motor cap on the forward direction take up reel. Like I said, I'm new at this.

Thanks again.

 

[audiojones]

Here's a dumb question: Do you have the auto shut-off switch set to "On" instead of "Auto" and can you verify that the power switch is operating properly?

The motor winding measurements won't do us much good without knowing what the impedance is supposed to be. The voltage measurements should be taken at the output of the transformer while the motor is under a load to see if they are the same from beginning to end (helps eliminate bad wiring and connector plugs). Also you want to measure across any switches or relay contacts to locate bad contacts. Any voltage readings other than zero across a set of closed energized contacts means those contacts are bad.

At this point I think I'd be looking for a donor deck to swap motors and transformers, it's hard to troubleshoot without knowing what the values are supposed to be.

 

[redpackman]

Nope, the auto shut off switch is set to "On."

But we have success.

I got a second machine that had a motor that would play in 7 1/2 ips, but didn't have the cleaning and touchup I've done on the sick machine trying to get it going. So I took the motor out of the new machine, put it in the first machine. Bingo. We have success and a machine that'll play in all three speeds. The fault was the capstan motor. Must be the windings for top speed that are shot, or something.

FWIW I noticed tonight working with the old motor before I took it out, that when I'd flick it from one of the lower speeds to top speed, once in awhile I could see some tiny sparks inside the motor. I'm pretty sure that's not good. It didn't happen all the time, just once or twice. Anyway, it's now playing in all three speeds. Both channels sound pretty good.

I haven't even tried the record circuit yet. Do I dare? Well, that's for another day in the life of a vintage equipment tinkerer.

Thank you audiojones. I would not have gotten near this far without you....or without setting myself on fire.

 

[audiojones]

Nice job! Yep, tiny sparks inside motor = not good, sounds like a motor winding has been compromised.

Try out the amp functions and see if you get lucky, but if the amp fails don't despair. The board uses some 2sc458 transistors that are notorious for failing. Modern substitutes for them are cheap and readily available and the job is fairly straightforward, so any amp troubles just ask.

Common symptoms are: one or both channels not recording, one or both channels not playing back, noises such as squealing, rustling, popping or hissing, one or both vu meters flicking wildly, one channel lower than the other etc.

They also used them in the auto reverse triggering system so if the machine starts reversing itself randomly it's likely to be another bad 2sc458 transistor at the root of the trouble.

 

[redpackman]

Thanks again, audiojones!!! You certainly know Akai tape decks!! (I'll probably be back).